Endometrial cancer (EMC) is a malignant disease with high mortality in women. About 50,000 women in USA are annually diagnosed with EMC and ~8200 women die of this disease yearly. Thus, it is urgent to study the key molecular drivers and suppressors of EMC initiation, growth and metastasis for identifying new diagnostic/prognostic markers and therapeutic targets. NCOA6, a coactivator that works with multiple classes of transcription factors (TFs) to potentiate gene expression, appears to be frequently mutated and down- regulated in EMCs. Conditional knockout (KO) of Ncoa6 in the mouse endometrial epithelial (EC) and stromal cells causes estrogen super sensitivity, uterine epithelial hyperplasia and spontaneous EMC development. KO of Ncoa6 only in the endometrial ECs also triggered EMC development. Ncoa6 KO decreases the expression of DUSP6 and PTPRF, two phosphatases that inhibit the MAPK and PI3K/AKT pathways. NCOA6 KO also increases the expression of PRKCD, a PKC kinase that activates the Raf-ERK pathway and simulates cell migration and chemotaxis. We hypothesize that NCOA6 is a novel tumor suppressor of EMC, and it functions through controlling estrogen, MAPK and PI3K/AKT stimulated EC proliferation and carcinogenesis. In Aim 1, we will define the specific role of NCOA6 in suppressing estrogen-promoted EMC development. Transgenic mice with and without endometrial Ncoa6 KO will be produced to examine how the loss of Ncoa6 function will trigger and promote spontaneous EMC development in the endometrium with and without Pten expression under different estrogen conditions. Transgenic mice with a Ncoa6 mutation that prevents Ncoa6 interact with ER? will also be generated to test whether Ncoa6 relies on the interaction with ER? to suppress estrogen- promoted EMC development. In Aim 2, we will dissect the basic cellular and molecular mechanisms responsible for NCOA6-mediated repression of EMC. Specifically, we will use both bioinformatic and experimental approaches to identify TFs working with NCOA6 to regulate DUSP6, PRPTF and PRKCD genes. We will also use EMC cell lines and xenograft tumor growth mouse models to define the functional impacts of NCOA6-regulated expression of these 3 genes on the activities of MAPKs and AKT and on the capabilities of EMC cell proliferation, migration, invasion and tumor growth. In Aim 3, we will define the NCOA6 expression profile and its prognostic value in clinical subtypes of human endometrial tumors. We will semi-quantitatively measure NCOA6 protein expression levels in these specimens and determine the correlation/association relationships between NCOA6 expression levels and tumor grades, tumor stages, disease recurrence time or survival rates. These studies should generate significant impacts by establishing NCOA6 as an EMC suppressor and exploring its working mechanisms. These studies may also suggest NCOA6 as a diagnostic and a prognostic marker for EMC progression and offer a pre-clinical concept of principle to restore the function of NCOA6 or its regulatory pathways as a therapeutic strategy.